The electric field due to a short electric dipole at a large distance $(r)$ from center of dipole on the equatorial plane varies with distance as :

In the given circuit, the current (I) through the battery will be

The de Broglie wavelength of an electron having kinetic energy $\mathrm{E}$ is $\lambda$. If the kinetic energy of electron becomes $\frac{E}{4}$, then its de-Broglie wavelength will be :

The height of transmitting antenna is $180 \mathrm{~m}$ and the height of the receiving antenna is $245 \mathrm{~m}$. The maximum distance between them for satisfactory communication in line of sight will be :

(given $\mathrm{R}=6400 \mathrm{~km})$